This invention relates to a scanning-type exposure apparatus suitably used for the manufacture of various electronic devices such as a liquid crystal display device and a semiconductor chip.
In one such conventional scanning-type exposure apparatus as disclosed in Japanese Patent Unexamined Publication No. 61-188933, a mask, serving as a master plate, and a light-sensitive substrate, serving as a member to be exposed (hereinafter referred to as "exposure member"), are positioned or registered with respect to each other, and then the mask and the light-sensitive substrate are moved (that is, subjected to a scanning operation) in unison relative to an optical projection system, so that an image of the mask is transferred to the light-sensitive substrate. In this exposure apparatus, the mask is supported horizontally, and a stage movable in directions X, Y and e is provided for the light-sensitive substrate. This stage requires a large stroke for stepping movement in a direction (direction X) perpendicular to the scanning direction.
In this conventional exposure apparatus, the mask and the light-sensitive substrate are placed on a carriage, and are scanningly moved relative to the optical projection system through the carriage, thereby exposing the whole of a pattern area. Recently, however, a pattern area has been increased in size, and there has now been increasingly used a method in which a plurality of liquid crystal panels are taken or formed from a single light-sensitive substrate. Under the circumstances, it has been necessary to increase the extent of exposure and to increase the scanning length. This has invited a problem that the size of the exposure apparatus itself has been increased. To overcome this problem, there has been proposed a so-called step-and-scan exposure method in which the pattern area is divided into a plurality of sections, and the scanning exposure is effected for each section in a separate manner. This method has been used in the manufacture of a device having a large single effective pattern area such as a liquid crystal device.
In the step-and-scan exposure method, however, the mask and the optical system must be steppingly moved relative to each other not only in the scanning direction but also in a direction perpendicular to the scanning direction (In some scanning methods, the light-sensitive substrate must also be moved relative to the mask). This not only makes the construction of the exposure apparatus complicated but also requires the mask and the light-sensitive substrate to be aligned with each other for each stepping motion so that highly precisely-adjoining exposure areas can be joined together. This adversely affects the throughput.
Furthermore, when the large mask corresponding to the large pattern area is supported horizontally, the mask is flexed or deflected due to its own weight, and because of this deflection the pattern image of the mask is shifted laterally, thus causing a shift error. This shift error adversely affects the precision of the exposure as described later.